Method and device for operating electric arc furnaces and/or resistance furnaces

ABSTRACT

The aim of the invention is to provide a means of also cooling the lower part of electric arc furnaces and/or resistance furnaces. To this end, said lower part—the actual melting vessel ( 4 )—is surrounded with a jacket ( 9 ) at a certain distance, forming a shell, and the resulting intermediate space is configured as a cooling device ( 10 ) and subjected to the action of a cooling medium ( 14 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and a device for operating electricarc melting furnaces and/or resistance melting furnaces, comprising amelting vessel for receiving the molten mass, whose lid and upperlateral wall are cooled by a cooling medium, preferably water, up to orinclusive of the area of the slag zone.

2. Description of the Related Art

Such cooled furnaces are known in many modifications. In these knownfurnaces, the furnace bottom is the only area that is not cooled and hasthe tendency to undergo increased wear of the refractory lining andrequire increased repair expenditure of the construction elements.

In order to cool at least that part of the furnace bottom in which thebottom electrodes are located, it is known from EP 02 03 301 B1 toarrange in this area of the furnace bottom at a spacing a plate throughwhich the necks of the electrodes or contact pins are guided and to blowair into the intermediate space between this plate and the furnacebottom. With this measure the bottom electrode is cooled during themelting and tapping operation wherein, for extended operationaldowntimes, the cooling efficiency can be adjusted, by reducing it, suchthat the rate of temperature change of the bottom electrode, inparticular, at the beginning or the end of the operating downtime, doesnot surpass predetermined maximum values.

SUMMARY OF THE INVENTION

Based on this known prior art, it is the object of the invention toprovide a method for operating electric arc melting furnaces andresistance melting furnaces with which the disadvantage of only apartial cooling can be prevented.

The above object is solved for electric arc melting furnaces andresistance melting furnaces of the described kind by a shell-shapedcooling device enclosing the lower part of the melting vessel and formedas a mantle corresponding to the contour of the outer furnace wall andarranged on the melting vessel at a spacing thereto, wherein at leastone inlet opening and at least one outlet opening for the cooling mediumare arranged on the cooling device.

By the measure of the invention to also cool the lower area of thefurnace, the furnace bottom and the lower part of the lateral walls, amore beneficial effect is achieved as a whole in regard to the servicelife of the refractory lining as well as of the additional constructionelements of the furnace. Moreover, with the measure the invention anadvantageous cooling action is also exerted onto the bottom electrode.

The cooling according to the invention is realized by means of ashell-shaped cooling device, enclosing the area of the lower furnace tobe cooled, through which the cooling medium flows. The cooling mediumcan be a gaseous material, for example, air, or a liquid material, forexample, water.

For maintaining flow of the cooling medium within the cooling device,convection can be used in the simplest case wherein, in the case of aircooling, the convection can be enhanced by a chimney which is connectedwith the outflow opening of the cooling device. With this chimney, it isadvantageously also prevented that flames can enter the cooling deviceduring tapping of the furnace.

Should convection not be sufficient, according to the invention it isalso possible to convey the cooling medium through the cooling device bymeans of a conveying device, for example, a pump or a blower, arrangedexternally to the cooling device. Particularly for liquid cooling media,it is beneficial to convey the cooling medium in a closed circuitthrough the cooling device. In this connection, the cooling medium whichhas been heated can be cooled advantageously such that a heat recoveryis possible.

The flow speed and the temperature of the cooling medium determine thecooling efficiency of the cooling device so that, according to anadvantageous embodiment of the invention, the cooling efficiency can bematched to the operating temperature of the furnace by changing theseparameters by means of a measuring and control device.

The cooling device which encloses the lower part of the furnace like ashell is formed according to the invention in a simple way. By means ofa sheet metal, which is shaped according to the furnace contour and isarranged on the furnace at a spacing thereto, a mantle-shaped hollowspace is provided through which the cooling medium flows. The hollowspace has at least one inlet opening and at least one outlet opening forthe cooling medium, wherein in the case of convection the inlet openingis to be expediently arranged centrally at the furnace bottom and theoutlet opening laterally at the top on the sidewalls. For a forced flowby means of a conveying device, the inlet and outlet openings can bearranged differently.

For improving the cooling action by means of the cooling medium, coolingribs, which are fastened on the furnace wall, for example, by welding,are arranged according to an advantageous embodiment of the inventionwithin the hollow space of the cooling device. These cooling ribs areconfigured such that they ensure an optimal cooling efficiency without,however, substantially increasing the flow resistance of the coolingdevice, for which purpose they are expediently curved in the flowdirection.

In order to realize the possibility of heat recovery for cooling in aclosed circuit, a heat recovery device is arranged in the coolingcircuit lines in addition to the conveying device for maintaining thecirculation, in which the heated cooling medium can be cooled and whichuses the heat released thereby, for example, by storing it.

According to one embodiment of the invention, a measuring and controlsystem, into which the measured values of the operating temperatures ofthe furnace are entered, is connected with this heat recovery device andwith the conveying device in order to be able to affect the temperatureand the quantity of the cooling medium flowing into the cooling device.

Further advantages, details and features of the invention will beexplained in the following in more detail by means of an embodimentschematically illustrated in the drawing figures.

It is shown in:

FIG. 1 a vertical section of a furnace;

FIG. 2 a block diagram of a cooling circuit.

FIG. 1 show schematically a furnace 1 with a furnace bottom 2, lowerlateral walls 3 on the melting vessel 4, upper lateral walls 5, and alid 6. The upper lateral walls 5 extend downwardly up to approximatelythe melting vessel 4 containing the molten mass and are provided in thisarea, like the lid 6, with a water cooling device 5′.

The melting vessel 4 has a refractory lining 8, illustrated by hatching,and is formed by the furnace bottom 2 and the lower lateral walls 3.According to the invention, the melting vessel 4 is surrounded at aspacing by a mantle 9, preferably of sheet steel, which is formedaccording to the contours of the outer furnace wall 7. The thusresulting shell-shaped hollow space forms the cooling device 10 throughwhich the cooling medium 14 flows.

The cooling medium enters in the illustrated embodiment by means of aninlet opening 12 centrally arranged at the furnace bottom 2, flows inthe direction of the arrow to the lateral walls 3, and then exits thecooling device 10 at the upper end of the sidewalls 3 through the outletopenings 13. A chimney 22 is connected to one of the outlet openings 13.Within the cooling device 10, cooling ribs 11, shaped corresponding tothe flow direction of the cooling medium 14, are arranged on the furnacewall 7 for improving heat transfer as well as for swirling the coolingmedium 14.

In FIG. 2 one embodiment of a cooling circuit is illustrated in the formof a block diagram. The cooling device 10 of the furnace 1 and themelting vessel 4 is connected at its outlet opening 13 via the outletline 16 with a heat recovery device 18. In this heat recovery device 18,the cooling medium 14 which has been heated during cooling of themelting vessel 4 is cooled with heat recovery. A conveying device 17,for example, a pump or a blower, which is arranged in the inlet line 15,forces the now cooled cooling medium exiting the heat recovery device 18back into the cooling device 10 via the inlet opening 12. A conveyingdevice 17 each may be arranged in the inlet line 15 and in the outletline 16.

The heat recovery device 18 and the conveying device 17 are connected bycontrol lines 21 with a measuring and control device 19 by which theconveying output of the conveying device 17 and the temperature of thecooling medium 14, in the heat recovery device 18, are controlled as afunction of the operating state of the furnace 1. For this purpose, themeasuring and control device 19 is connected by means of a measured dataline 20 with corresponding measuring devices on the furnace (themeasuring devices are not illustrated).

The invention is not limited to the embodiments illustrated in thedrawing figures which, for improving the illustration, have been shownwith an over-sized cooling device. Depending on the configuration andoperational conditions of the furnace, according to the invention theshape and size of the cooling device, the number and arrangement of theinlet and outlet openings as well as the connection of the coolingdevice with other devices (measuring and control unit, conveying deviceetc.) can be configured variably when the basic principle of theinvention is obeyed according to which an optimal cooling of the entiremelting vessel is to be realized in a simple way with a construction andcost expenditure as minimal as possible.

What is claimed is:
 1. A resistance melting furnace, comprising: amelting vessel having a refractory lining and an outer furnace wall, themelting vessel having a furnace bottom and lower lateral walls; an upperpart cooled by a first cooling medium and comprising a lid and upperlateral walls; a shell-shaped cooling device enclosing the outer furnacewall, wherein a second cooling medium flows through the cooling deviceand is in direct contact with the outer furnace wall, wherein the secondcooling medium is transported in the cooling device by convection, aconveying device arranged externally on the cooling device andconfigured to convey the second cooling medium in addition to theconvection of the second cooling medium.
 2. The resistance meltingfurnace according to claim 1, wherein the cooling device has a mantlehaving a contour corresponding to a contour of the outer furnace wall,wherein the mantle is arranged on the melting vessel, wherein thecooling device has at least one inlet opening and at least one outletopening for the second cooling medium.
 3. The resistance melting furnaceaccording to claim 2, wherein the inlet opening is arranged centrally atthe furnace bottom and the outlet opening is arranged laterally at anupper end of the lower lateral walls.
 4. The resistance melting furnaceaccording to claim 1, further comprising a conveying device arrangedexternally on the cooling device and configured to convey the secondcooling medium.
 5. The resistance melting furnace according to claim 1,wherein the second cooling medium flows in a closed circuit through thecooling device.
 6. A resistance melting furnace, comprising: a meltingvessel having a refractory lining and an outer furnace wall, the meltingvessel having a furnace bottom and lower lateral walls; an upper partcooled by a first cooling medium and comprising a lid and upper lateralwalls; a shell-shaped cooling device enclosing the outer furnace wall,wherein a second cooling medium flows through the cooling device and isin direct contact with the outer furnace wall, wherein the coolingdevice has cooling ribs arranged on the outer furnace wall.
 7. Aresistance melting furnace, comprising: a melting vessel having arefractory lining and an outer furnace wall, the melting vessel having afurnace bottom and lower lateral walls; an upper part cooled by a firstcooling medium and comprising a lid and upper lateral walls; ashell-shaped cooling device enclosing the outer furnace wall, wherein asecond cooling medium flows through the cooling device and is in directcontact with the outer furnace wall, further comprising: a heat recoverydevice, wherein the cooling device comprises an outlet line and an inletline, wherein the heat recovery and the cooling device are connected toone another via the inlet line and the outlet line and form a closedcircuit; and at least one conveying device arranged in at least one ofthe inlet line and the outlet line.
 8. The resistance melting furnaceaccording to claim 7, wherein the at least one conveying device is ablower or a pump.
 9. The melting furnace according to claim 7, furthercomprising a measuring and control device having control lines and ameasured data line, wherein at least one of the heat recovery device andthe conveying device are connected by the control lines to the measuringand control device, wherein the measuring and control device is adaptedto receive measured values of an operating temperature of the electricarc melting furnace or resistance melting furnace via the measured dataline.
 10. The resistance melting furnace according to claim 2, whereinthe outlet opening is connected to a chimney for air convection cooling.